The present application relates to an optical body, a window member, a fitting, and a solar shading device, which can suppress change in color tone.
Recently, there have been increased the cases of coating layers for partly absorbing or reflecting the sunlight on architectural glasses for high-rise buildings and housings, vehicular window glasses, etc. Such a trend represents one of energy-saving measures with the view of preventing global warming, and it is intended to reduce a load of cooling equipment, which is increased with solar energy, i.e., the sunlight, entering the indoor through windows and raising the indoor temperature. Optical energy incoming from the sun is primarily given by light in a visible range at wavelengths of 380 to 780 nm and light in a near infrared range at wavelengths of 780 to 2100 nm. Because transmittance of the light in the latter near infrared range through windows is unrelated to visibility of human eyes, the transmittance of the near infrared light is an important factor affecting the performance that is to be provided by a window having high transparency and a high thermal shielding ability.
As an example of methods for cutting off the light in the near infrared range while maintaining transparency to the light in the visible range, there is a method of providing, on a window glass, an optical body having a high reflectance in the near infrared range. With regards to such a method, a technique using, as a reflecting layer, an optical multilayer film is disclosed (see, e.g., Japanese Unexamined Patent Application Publication No. 2007-152773). However, the reflecting layer used in the disclosed technique is formed on a flat film or a flat window glass, and the incident sunlight is just specularly (regularly) reflected. Therefore, the light incoming from the sky and specularly reflected by the flat film or window glass reaches other buildings and the ground in the nearby outside where the light is absorbed and converted to heat, thus raising the ambient temperature. Accordingly, a local temperature rise occurs in the surroundings of a building in which all windows are coated with the above-mentioned type of reflecting layer. This gives rise to the problems that, in urban areas, a heat island phenomenon is accelerated and grass does not grow in areas irradiated with the reflected light.